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From:   Roman Kagan <rkagan@virtuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
CC:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?iso-8859-2?Q?Radim_Kr=E8m=E1=F8?= <rkrcmar@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
Subject: Re: [PATCH v2 3/4] x86/kvm/hyper-v: direct mode for synthetic timers
Thread-Topic: [PATCH v2 3/4] x86/kvm/hyper-v: direct mode for synthetic timers
Thread-Index: AQHUhZ9mV1oam64KnkyNE5PKjfame6V4KKWA///bCACAAAeggA==
Date:   Mon, 10 Dec 2018 13:21:39 +0000
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On Mon, Dec 10, 2018 at 01:54:18PM +0100, Vitaly Kuznetsov wrote:
> Roman Kagan <rkagan@virtuozzo.com> writes:
> > Just noticed that the patch seems to assume that "direct" timers are
> > allowed to use any vectors including 0-15.  I guess this is incorrect,
> > and instead stimer_set_config should error out on direct mode with a
> > vector less than HV_SYNIC_FIRST_VALID_VECTOR.
>=20
> The spec is really vague about this and I'm not sure that this has
> anything to do with HV_SYNIC_FIRST_VALID_VECTOR (as these are actually
> not "synic" vectors, I *think* that SynIC doesn't even need to be
> enabled to make them work).
>=20
> I checked and Hyper-V 2016 uses vector '0xff', not sure if it proves
> your point :-)
>=20
> Do you envision any issues in KVM if we keep allowing vectors <
> HV_SYNIC_FIRST_VALID_VECTOR?

It's actually lapic that treats vectors 0..15 as illegal.  Nothing
Hyper-V specific here.

Roman.